JP2021055077A - Biaxially oriented polyester film - Google Patents

Abstract

To provide a biaxially oriented polyester film that is excellent in runnability and take-up performance, and, furthermore, is excellent in dimensional stability, and, when used as a magnetic recording medium, that produces a high-density magnetic recording medium having a smooth magnetic layer as well as having a small dimensional change due to the environmental change in temperature or humidity, and the storage, and having a low error rate.SOLUTION: The problem is solved by a biaxially oriented polyester film in which the humidity-expansion coefficient in film width direction is 4.5 to 6.5 ppm/%RH, the temperature-expansion coefficient in the width direction is -3 to 7 ppm/°C, and, on at least one outermost layer surface, the number of protrusions with a height of 60 nm or more is 0 to 200/mm2.SELECTED DRAWING: None

Description

The present invention relates to a biaxially oriented polyester film having excellent dimensional stability and surface properties, and relates to a biaxially oriented polyester film that can be suitably used as a base film for a coating type magnetic recording medium such as a data storage. is there.

Biaxially oriented polyester films are used in various applications due to their excellent thermal properties, dimensional stability, mechanical properties, and easy control of surface morphology, and are particularly useful as supports for magnetic recording media and the like. Are known. High-density recording is always required for magnetic recording media.

There are generally three methods for achieving high-density recording: increasing the number of tracks, shortening the recording wavelength, and increasing the tape length.

As the number of tracks increases, the width of one track becomes narrower, and a slight dimensional change causes data loss. Therefore, it is important to control the dimensional stability in the tape width direction. Such dimensional changes can be divided into irreversible changes such as heat shrinkage and reversible changes such as expansion and contraction due to temperature and humidity. It is preferable that there is no irreversible change, but it can be removed by a treatment such as annealing in the processing step. On the other hand, since reversible changes cannot be easily removed, if the temperature and humidity change during storage, the film expands and contracts, and the recorded data deviates from the original position, making it unreadable. is there.

Further, in order to realize sufficient electromagnetic conversion characteristics after shortening the recording wavelength, surface smoothness is required, and further, thinning of the magnetic layer and smoothness of the surface of the magnetic layer by using a fine particle magnetic material are required. It is effective to further improve.

In recent years, supports for magnetic recording media using ferromagnetic hexagonal ferrite powder have thinned magnetic layers, non-magnetic layers, backcoat layers, and the supports themselves, so that not only smooth surfaces but also running surfaces Roughening is restricted. When stored in a roll state as a magnetic recording medium in the manufacturing process, the protrusions formed on the running surface are transferred to the magnetic surface to form dents on the smooth magnetic layer surface, or the support becomes thinner as the support becomes thinner. There is a problem that an error signal (missing pulse) is generated because the large particles contained in the magnetic layer are pushed up to the smooth surface and a gentle convex swell is generated on the surface of the magnetic layer to reduce the smoothness of the surface of the magnetic layer. .. If the diameter of the particles contained in the support is reduced in order to improve the smoothness of the surface of the magnetic layer and the smoothness is improved as an ultra-high-definition surface, the running performance, winding, and surface durability are insufficient. It becomes. Therefore, it can be said that the demand for improving the characteristics such as both slitting property and surface smoothness is a problem that always occurs for high-density recording.

In order to solve the above problems, polyester films having excellent dimensional stability in a temperature and humidity range capable of responding to all environmental changes (for example, Patent Documents 1 and 2) have been studied. However, the actual situation is that the surface of the support for ensuring the smoothness of the surface of the magnetic layer using a thin magnetic layer or a fine particle magnetic material such as ferromagnetic hexagonal ferrite powder has not been obtained. In addition, a polyester film that is excellent in humidity expansion and has both running performance and smoothness by controlling the number of protrusions at a specific height (for example, Patent Documents 3 and 4) has both dimensional stability against heat and rigidity of the film. There is a polyester film (for example, Patent Document 5).

Japanese Unexamined Patent Publication No. 2005-163020 Japanese Unexamined Patent Publication No. 2015-25047 Japanese Unexamined Patent Publication No. 2016-79410 JP-A-2018-150463 Japanese Unexamined Patent Publication No. 2000-141475

However, neither of them considers temperature expansion at all, and has not reached a film having excellent dimensional changes in all temperature and humidity regions from room temperature to high temperature and humidity.

An object of the present invention is biaxial orientation having excellent dimensional stability in all temperature and humidity regions of low temperature and low humidity, low temperature and high humidity, high temperature and low humidity, and high temperature and high humidity, and also having excellent surface smoothness and slit property. The purpose is to provide a stable polyester film.

The present invention for solving the above problems is characterized by the following configurations.

(1) The coefficient of thermal expansion in the width direction is 4.5 to 6.5 ppm /% RH, the coefficient of thermal expansion in the width direction is -3.0 to 7.0 ppm / ° C., and on at least one outermost layer surface. A biaxially oriented polyester film having a height of 60 nm or more and a number of protrusions of 0 to 200 / mm ^2.

(2) The biaxially oriented polyester film according to (1) above, wherein the heat shrinkage rate in the width direction is 1.0% or less.

(3) The biaxially oriented polyester film according to (1) or (2) above, wherein the Young's modulus in the width direction is 7.0 to 12.0 GPa.

(4) The biaxially oriented polyester film according to any one of (1) to (3) above, wherein the minute melting peak temperature (T-meta) is 210 to 240 ° C.

(5) The biaxially oriented polyester film according to any one of (1) to (4) above, wherein at least one surface roughness (Sa1) is 3.0 to 7.0 nm.

(6) The biaxially oriented polyester film according to (5) above, wherein the surface roughness (Sa2) of the outermost layer surface on the side opposite to the surface constituting Sa1 is 0.5 to 5.0 nm.

(7) The biaxially oriented polyester film according to any one of (1) to (6) above, which is used as a base film for a magnetic recording medium of a coating type digital recording method.

The biaxially oriented polyester film of the present invention is a biaxially oriented polyester film having excellent dimensional stability in all temperature and humidity regions such as slit property, low temperature and low humidity, low temperature and high humidity, high temperature and low humidity, and high temperature and high humidity, and is magnetic. To obtain a biaxially oriented polyester film that has a smooth magnetic layer when used as a recording medium, has a small dimensional change due to environmental changes in temperature and humidity and storage, and is a high-density magnetic recording medium in which the generation of missing pulses is suppressed. Can be done.

It is the schematic of the film dimension measuring apparatus.

As the polyester used in the present invention, for example, a polymer composed of an acid component such as an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid, or a polymer having a diol component as a constituent unit (polymerization unit) is used. Can be done. Further, the polyester film referred to in the present invention represents a film in which the main component constituting the film is polyester.

Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-diphenyldicarboxylic acid. Acids, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenylsulfone dicarboxylic acid and the like can be used, and among them, terephthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid can be used. .. As the alicyclic dicarboxylic acid component, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecandioic acid and the like can be used. Only one kind of these acid components may be used, or two or more kinds thereof may be used in combination.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1 , 6-Hexanediol, 1,2-Cyclohexanedimethanol, 1,3-Cyclohexanedimethanol, 1,4-Cyclohexanedimethanol, Diethylene glycol, Triethylene glycol, Polyalkylene glycol, 2,2'-bis (4'-) β-Hydroxyethoxyphenyl) propane and the like can be used, and among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like can be preferably used, and ethylene glycol is particularly preferable. Etc. can be used. Only one kind of these diol components may be used, or two or more kinds thereof may be used in combination.

The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, or may be trifunctional such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol and 2,4-dioxybenzoic acid. Compounds and the like may be copolymerized within a range in which the polymer is substantially linear without excessive branching or cross-linking. Further, in addition to the acid component and the diol component, the present invention comprises aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, and p-aminophenol and p-aminobenzoic acid. If the amount is so small that the effect of the above is not impaired, further copolymerization can be performed.

The copolymerization ratio of the polymer can be examined by using an NMR method (nuclear magnetic resonance method) or a microscopic FT-IR method (Fourier transform microinfrared spectroscopy).

As the polyester, a polyester having a glass transition temperature of less than 150 ° C. can be preferably used in order to be able to perform biaxial stretching and to exhibit the effects of the present invention such as dimensional stability. The polyester used in the present invention is preferably polyethylene terephthalate or polyethylene naphthalate (polyethylene-2,6-naphthalate), and may be a copolymer or modified product thereof, or may be a polymer alloy with another thermoplastic resin. .. The polymer alloy referred to here is a polymer multi-component system, and may be a block copolymer by copolymerization or a polymer blend by mixing or the like. As the polyester used in the present invention, it is more preferable that the main component is polyethylene terephthalate because a process for increasing the crystallite size and the degree of crystal orientation can be easily applied. Here, the main component means that it is 80% by mass or more in the film composition.

When the polyethylene terephthalate used in the present invention is a polymer alloy, the other thermoplastic resin is preferably a polymer compatible with polyester, more preferably a polyetherimide resin or the like. As the polyetherimide resin, for example, those shown below can be used.

(However, in the above formula, R ₁ is a divalent aromatic or aliphatic residue _{having 6 to 30 carbon atoms, and R 2} is a divalent aromatic residue having 6 to 30 carbon atoms. From the group consisting of an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 2 to 20 carbon atoms, and a polydiorganosiloxane group chain-terminated with an alkylene group having 2 to 8 carbon atoms. It is a selected divalent organic group.)
Examples of the above R ₁ and R ₂ include aromatic residues represented by the following formula group.

(N is an integer of 2 or more, preferably an integer of 20 to 50.)
In the present invention, from the viewpoint of affinity with polyester, cost, melt moldability, etc., 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m-phenylenediamine, or A polymer having a repeating unit represented by the following formula, which is a condensate with p-phenylenediamine, is preferable.

Or

This polyetherimide is available from SABIC Innovative Plastics under the trade name of "Ultem", and is "Ultem® 1000", "Ultem® 1010", "Ultem® 1040". , "Ultem® 5000", "Ultem® 6000" and "Ultem® XH6050" series and registered trademark names of "Extem® XH" and "Extem® UH" Etc. are known.

In the present invention, for example, as a method of mixing polyester and polyimide, a method of pre-melting and kneading (pelletizing) a mixture of polyester and polyimide to form a master chip before melt extrusion, or a method of mixing and melting during melt extrusion. There is a method of kneading. Among them, a method of pre-kneading using a high shear mixer such as a twin-screw extruder to which a shear stress is applied to form a master chip is preferably exemplified. In that case, the mixed master chip raw material may be put into a normal uniaxial extruder to form a melt film, or the sheet may be directly seated without being made into a master chip with high shear added. When mixing with a twin-screw extruder, those equipped with a three-row twin-screw type screw or a two-screw twin-screw type screw are preferable from the viewpoint of reducing defective dispersion. Further, when polyester and polyimide are mixed, it is preferable to prepare a master chip in which a polyimide resin is mixed at a high concentration because there is a difference in melt viscosity. In particular, the mixed weight ratio of polyester / polyimide is 10/90 to It is preferably 70/30, and a more preferable range is the range of 30/70 to 60/40.

In the present invention, the content of the polyimide resin in the polyester film is preferably 0.1% by weight or 20% by weight, more preferably 3% by weight or more and 15% by weight or less, still more preferably, based on the entire film. It is 5% by weight or more and 10% by weight or less. If the content exceeds the upper limit, the coefficient of thermal expansion in the width direction of the present invention may not be obtained.

The humidity expansion coefficient in the width direction of the biaxially oriented polyester film of the present invention is 4.5 to 6.5 ppm /% RH, preferably 5.0 to 6.0 ppm /% RH. If the coefficient of thermal expansion is larger than 6.5 ppm /% RH, the film expands in the width direction in response to changes in humidity in an environment in which magnetic data is recorded and reproduced, so that reproduction failure is likely to occur. Further, when the coefficient of thermal expansion is smaller than 4.5 ppm /% RH, it may be difficult to control the coefficient of thermal expansion of the film within the range of the present application. The coefficient of expansion of humidity in the width direction can be controlled by the stretching ratio in the width direction shown later. When the stretching ratio is increased, the coefficient of thermal expansion decreases. However, if the stretching ratio in the width direction is increased, the temperature expansion coefficient may become too small together with the humidity expansion coefficient, so it is important to adjust the stretching ratio and the heat-fixing temperature.

The coefficient of thermal expansion in the width direction of the biaxially oriented polyester film of the present invention is −3.0 to 7.0 ppm / ° C., preferably −2.0 to 5.0 ppm / ° C. When the coefficient of thermal expansion is less than −3.0 ppm / ° C., the film shrinks in the width direction with respect to the temperature change in the environment for recording / reproducing magnetic data. On the other hand, since the magnetic head expands (usually 7 ppm / ° C.) with respect to a temperature change, mutual dimensional changes become too large, and reproduction defects are likely to occur. If the coefficient of thermal expansion exceeds 7.0 ppm / ° C, the coefficient of thermal expansion cannot be controlled within the range of the present application, and the film expands in the width direction in response to changes in the temperature and humidity of the environment in which magnetic data is recorded and reproduced. It is easy to cause defects. The coefficient of thermal expansion in the width direction can be controlled by the stretching ratio in the width direction shown later. When the stretching ratio is increased, the coefficient of thermal expansion decreases. In order to keep the temperature and the coefficient of thermal expansion in the width direction of the present invention within the range of the present invention, it is important to adjust the stretching ratio in the width direction and the heat-fixing temperature. Further, containing the polyetherimide in a proportion of 2 to 20% by weight or less, preferably 3 to 15% by weight or less, more preferably 5 to 10% by weight or less in the film is the temperature in the width direction of the present invention. It is preferable because the humidity expansion coefficient can be easily obtained.

On the surface of at least one outermost layer of the biaxially oriented polyester film of the present invention, the number of protrusions having a height of 60 nm or more is 0 to 200 / mm ² , preferably 0 to 150 / mm ² , and more preferably 0 to 100. / Mm ² . If the number of protrusions having a height of 60 nm or more ^{exceeds 200 / mm 2} , the smoothness of the surface may deteriorate and a missing pulse may be generated.

The number of protrusions at a height of 60 nm in the present invention described above is the number of protrusions at a height of 60 nm from the reference plane determined by scanning white interference microscope measurement. When the number of protrusions ^{exceeds 200 / mm 2} , for example, when the tape is wound as a magnetic recording tape, the unevenness on the surface of the backcoat layer is transferred to the surface of the magnetic layer, so that the number of transfer marks increases and a missing pulse is generated. The frequency may increase.

The heat shrinkage in the width direction of the biaxially oriented polyester film of the present invention is preferably 1.0% or less. When the heat shrinkage rate in the width direction exceeds 1.0%, the film shrinks in the width direction in the processing process of the magnetic recording medium, wrinkles are generated on the surface of the magnetic recording medium, and the smoothness of the surface of the magnetic layer is lowered. Sometimes.

The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the width direction of 7.0 to 12.0 GPa, and the Young's modulus in the width direction is 7.0 to 11.0 GPa from the viewpoint of controlling the coefficient of thermal expansion in the width direction. More preferred from. When the Young's modulus in the width direction is within the above range, the dimensional stability tends to be good due to environmental changes during recording and reproduction of the magnetic recording medium when used for a magnetic recording medium. Young's modulus in the width direction can be controlled by the temperature and magnification of TD stretching 1 and 2 described later. In particular, the total TD magnification has an effect, and the higher the total TD magnification, the higher the TD Young's modulus.

The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the longitudinal direction of 3.5 to 8.0 GPa. When the Young's modulus in the longitudinal direction is within the above range, the storage stability due to the tension during storage of the magnetic recording medium becomes better when used for the magnetic recording medium. A more preferable range of Young's modulus in the longitudinal direction is 3.8 to 7.0 GPa, and a further preferable range is 4.0 to 6.0 GPa. Young's modulus in the longitudinal direction can be controlled by the MD draw ratio. The higher the MD magnification, the higher the MD Young's modulus.

The micromelting peak temperature (T-meta) of the biaxially oriented polyester film of the present invention is preferably 210 to 240 ° C, more preferably 220 to 235 ° C. If the minute melting peak temperature is less than 210 ° C., the structure of the biaxially oriented polyester film may be insufficiently fixed, and it may be difficult to control the coefficient of thermal expansion within the range of the present application. Further, when the minute melting peak temperature exceeds 240 ° C., the TD orientation relaxation is promoted too much, so that the coefficient of thermal expansion becomes too large and the dimensional stability deteriorates. Further, since the smoothness of the surface is lowered, it becomes difficult to control the surface roughness and the height of protrusions of the present invention.

The surface roughness (Sa1) of at least one of the outermost layer surfaces of the biaxially oriented polyester film of the present invention is preferably 3.0 to 7.0 nm, more preferably 3.0 to 5.0 nm. In order to satisfy the object of the present invention, it is preferable that the surface functions as a surface which is responsible for running and slitting properties. If the surface roughness (Sa1) is less than 3.0 nm, the running performance and slitting property are likely to be poor, and if the surface roughness (Sa1) exceeds 7.0 nm, the smoothness of the magnetic layer surface when used as a magnetic recording medium. Missing pulses are likely to occur frequently due to the decrease.

Further, the surface roughness (Sa2) of the outermost layer surface on the side opposite to the surface constituting the above-mentioned Sa1 is preferably smaller than the above-mentioned surface roughness (Sa1), in order to satisfy the missing pulse of the present invention. It is preferable to apply a magnetic layer on the surface side of the surface. The surface roughness (Sa2) is preferably 0.5 to 5.0 nm, more preferably 0.5 to 3.0 nm. If the surface roughness (Sa2) is out of the above range, it may be difficult to achieve both running performance, slitting property, and missing pulse when a magnetic layer is provided on the surface and used as a magnetic recording medium.

In order to control the surface roughness (Sa1) and (Sa2) of the present invention, respectively, the inert particles having an average primary particle size of 0.01 to 0.3 μm are within the range of 0.01 to 0.5% by mass. It is preferable to have a laminated structure of two or more layers having at least one layer (B layer) contained in. In this case, the B layer functions as a layer responsible for running performance, is provided as one outermost layer of the film, and is provided with a layer (A layer) responsible for smoothness on the other outermost layer. When the A layer contains inert particles, it is preferable to use particles having an average primary particle size of 0.01 to 0.1 μm because the surface roughness (Sa2) of the present invention can be easily controlled. The content of the inert particles can be added in the range of 0.01 to 0.2% by mass. The biaxially oriented polyester film of the present invention has a laminated structure of at least two layers, so that it becomes easy to control the smoothness of the surfaces of both outermost layers, and it is possible to achieve both excellent surface smoothness, running performance and slitting property. It is preferable because it can be done.

In the biaxially oriented polyester film of the present invention, it is preferable that the outermost layer having the above-mentioned number of protrusions having a height of 60 nm or more and having a surface roughness (Sa1) of 3.0 to 7.0 nm is the B layer. ..

As a method for controlling the number of protrusions having a height of 60 nm or more in the present invention, it is possible to control by the average primary particle diameter of the contained particles in the B layer, the addition amount, the stacking thickness, and the heat fixing temperature. In particular, it is important to use two or more kinds of particles having an average primary particle diameter of 0.3 μm or less, preferably 0.01 to 0.2 μm, having different average primary particle diameters contained in the B layer.

The particles preferably contained in the B layer of the biaxially oriented polyester film of the present invention are not particularly limited, but either inorganic particles or organic particles can be used. Specific types include inorganic particles such as clay, mica, titanium oxide, calcium carbonate, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina silicate, kaolin, talc, montmorillonite, alumina, and zirconia. , Acrylic acids, styrene resin, silicone, imide and other organic particles, core-shell type organic particles, etc. can be exemplified. However, in order to control the protrusion height and the number of protrusions having a height of 60 nm or more in the present invention, simply Organic particles and colloidal silica, which are spherical particles that are monodisperse, are particularly preferable. Further, it is preferable to add alumina particles to the B layer in order to improve the phototaxis and the slit property because it can be efficiently improved.

The content of the particles added to the B layer of the biaxially oriented polyester film of the present invention is preferably 0.005 to 0.8% by mass, more preferably 0.01 to 0.5% by mass.

The laminated thickness (t) of the B layer of the biaxially oriented polyester film of the present invention is preferably 1 μm or less, more preferably 0.6 μm or less. When the laminated thickness is 1 μm or more, it may be difficult to control the number of protrusions having a height of 60 nm or more within the range of the present invention.

In producing the biaxially oriented polyester film of the present invention, it is important to carry out stepwise high temperature heat fixing by dividing the heat fixing temperature into two or more steps within the range of 190 to 235 ° C. The protrusion height and surface roughness tend to increase as the heat fixing temperature rises, but by adopting stepwise high-temperature heat fixing, it is possible to suppress the increase in protrusion height and surface roughness due to high-temperature heat fixing. It will be possible. Further, if the heat fixing temperature is set high, the orientation is easily relaxed, so that the humidity expansion coefficient in the width direction of the present application may not be controlled. However, by adopting the stepwise high temperature heat fixing, the orientation in the width direction is particularly large. The relaxation becomes gradual, and the coefficient of thermal expansion of the present application can be controlled within a preferable range.

The thickness of the biaxially oriented polyester film of the present invention is preferably in the range of 3.5 to 4.6 μm. When the thickness is smaller than 3.5 μm, the rigidity and dimensional stability are deteriorated, the waist of the tape is insufficient, and the electromagnetic conversion characteristics tend to be deteriorated when used as a magnetic recording medium. In addition, it becomes difficult to suppress the particles contained in the B layer from being pushed up toward the smooth surface (A surface). Further, if it is larger than 4.6 μm, the tape length per roll of the tape becomes short, so that it is difficult to cope with the miniaturization and high capacity of the magnetic tape. As a method of adjusting the thickness, the discharge amount of the screw at the time of melt extrusion of the polymer during the film formation of the biaxially oriented polyester film is adjusted, and the thickness of the unstretched film is controlled from the base to control the film after biaxial stretching. The thickness can be adjusted.

When the biaxially oriented polyester film of the present invention is used as a base film for a magnetic recording medium, it is necessary to provide a back coat layer (hereinafter referred to as BC layer) on the surface (B surface) side of the B layer side described above for high-density magnetic recording. It is preferable to obtain a medium. In magnetic recording media using ferromagnetic hexagonal ferrite powder for the magnetic layer, not only the base film but also the thickness of the magnetic layer, the non-magnetic lower layer, and the BC layer itself tend to be thinned. In particular, when the thickness of the BC layer is reduced to 0.4 μm or less, the surface of the BC layer is easily affected by the protrusions caused by the support, and the smoothness of the surface of the BC layer is lowered. By defining the number of protrusions at a specific height on the surface of the B layer within the scope of the present invention, even a thinner BC layer has an excellent electromagnetic wave generation frequency without impairing the smoothness of the surface. Can demonstrate conversion characteristics.

The biaxially oriented polyester film of the present invention as described above is produced, for example, as follows.

First, polyester pellets are melted using an extruder, discharged from a mouthpiece, cooled and solidified, and formed into a sheet. At this time, it is preferable to filter the polymer with a fiber-sintered stainless metal filter in order to remove unmelted matter in the polymer.

Various additives such as compatibilizers, plasticizers, weather resistant agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, and colorants, as long as they do not interfere with the characteristics of the present invention. , Conductive agents, crystal nucleating agents, ultraviolet absorbers, flame retardants, flame retardants, pigments, dyes, etc. may be added.

Subsequently, the sheet is simultaneously biaxially stretched in the longitudinal direction and the width direction, and then stretched again in the lateral direction for heat treatment. It is preferable to carry out simultaneous biaxial stretching because it becomes easy to control the number of protrusions and the height of protrusions having a height of 60 nm or more according to the present invention.

As the stretching type, a method of simultaneously biaxially stretching and then further stretching in the width direction is preferable. In the sequential biaxial stretching method, after stretching in the longitudinal direction, stretching stress tends to concentrate on the particle portion when stretching in the width direction, so that the protrusion height tends to increase. Furthermore, voids are more likely to be formed, which may cause tearing during stepwise high-temperature heat fixation. Further, if the orientation in the width direction becomes too high, it may be difficult to control the coefficient of thermal expansion within the range of the present invention.

Hereinafter, the method for producing a film of the present invention will be described as a representative example in which polyethylene terephthalate (PET) is used as a polyester. The present invention is not limited to the PET film, and may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalene dicarboxylate having a high glass transition temperature or melting point, extrusion or stretching may be performed at a temperature higher than the temperatures shown below.

First, PET pellets are produced. PET is manufactured by one of the following processes. That is, (1) a process in which terephthalic acid and ethylene glycol are used as raw materials, a low molecular weight PET or oligomer is obtained by a direct transesterification reaction, and then a polymer is obtained by a polycondensation reaction using an antimony trioxide or a titanium compound as a catalyst. , (2) A process in which a low molecular weight substance is obtained by a transesterification reaction using dimethyl terephthalate and ethylene glycol as raw materials, and then a polymer is obtained by a polycondensation reaction using an antimony trioxide or a titanium compound as a catalyst.

In order to contain the particles in the PET constituting the film, a method in which the particles are dispersed in ethylene glycol in a predetermined ratio in the form of a slurry and the ethylene glycol is added at the time of polymerization is preferable. When adding the particles, for example, if the particles of the water slurry or alcohol slurry obtained during the synthesis of the particles are added without being dried once, the dispersibility of the particles is good. Here, in order to control the number of protrusions having a height of 60 nm or more within the range of the present invention, it is important to keep the slurry concentration of the particles to 5% by mass or less. When the particles to be added are inorganic particles, glass beads having an average particle size of 0.5 to 0.05 mm may be added to the particle-containing slurry adjusted to a specific concentration, and the mixture may be stirred at 1,000 to 5,000 rpm for 1 to 5 hours. Very effective.

Next, the aqueous slurry of particles is directly mixed with PET pellets and kneaded into PET using a bent twin-screw kneading extruder so that the particle content is 0.1 to 0.5% by mass. Particle master pellets Is especially important to create. As a method for adjusting the particle content, a method of diluting the particle master pellets having a specific concentration prepared by the above method with PET which does not substantially contain particles at the time of film formation to adjust the particle content is preferable. At this time, the dispersibility of the particles is improved by setting the blending ratio of the PET pellets containing substantially no particles to 50% by mass or less, preferably 35% by mass or less, and the number of protrusions having a height of 60 nm or more according to the present invention. It becomes easier to control. It is also particularly important because it leads to reduction of film tear due to high-temperature heat fixation. Further, when two or more kinds of particle master pellets are used, the dispersibility of the particles is improved by using the two-stage kneaded particle master which is melt-kneaded again after blending in advance so as to have a predetermined desired content. It is preferably exemplified because the film tearing during the stepwise high temperature stretching is reduced.

Next, the obtained PET pellets are dried under reduced pressure at 180 ° C. for 3 hours or more, and then supplied to an extruder heated to 270 to 320 ° C. under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease. , Extruded from a slit-shaped die and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various filters, for example, high-precision filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh, in order to remove foreign substances and altered polymers. Further, it is extremely preferable to provide a gear pump in order to improve the quantitative supply property and obtain a desired laminated thickness in order to form the above-mentioned characteristic surface. To laminate the films, a plurality of different polymers may be fused and laminated using two or more extruders and manifolds or merging blocks.

Next, a method of simultaneously biaxially stretching the unstretched film thus obtained and then stretching again in the width direction will be described.

In the present invention, MD indicates the longitudinal direction (longitudinal direction) of the biaxially oriented polyester film, and TD indicates the width direction (horizontal direction) of the biaxially oriented polyester film.

First, the unstretched film is simultaneously biaxially stretched in the MD and TD directions. The stretching temperature varies depending on the type of polymer used, but can be determined using the glass transition temperature (Tg) of the unstretched film as a guide. It is preferably in the range of Tg + 20 ° C. to Tg + 50 ° C., more preferably Tg + 20 ° C. to Tg + 30 ° C. If the stretching temperature is lower than the above range, the film may be torn frequently and the productivity may be lowered, and it may be difficult to stably stretch the film when it is stretched again in the width direction after simultaneous biaxial stretching. The MD stretching ratio at the time of simultaneous biaxial stretching is 3 to 6 times, preferably 3.1 to 5.0 times. The TD stretching ratio is 3.3 to 6 times, preferably 3.5 to 5 times.

Next, stretching in the TD direction (TD stretching 2) is performed again. The stretching temperature of TD stretching 2 is 180 to 220 ° C, preferably 190 to 210 ° C. The draw ratio of TD stretch 2 is preferably 1.3 to 2 times, more preferably 1.4 to 1.7 times. If the stretching ratio or stretching temperature of TD stretching 2 is outside the range of the present invention, the coefficient of thermal expansion may not be controlled within the range of the present application. Further, at this time, simultaneous biaxial stretching within the range of 1.05 to 1.3 times in the MD direction has an effect of suppressing the surface protrusions on the B surface from being excessively connected in the TD direction when re-stretching in the TD direction. .. The area magnification is 12 to 30 times, preferably 14 to 25 times. If the area magnification is out of the range of the present application, it may be difficult to achieve both the coefficient of thermal expansion and the coefficient of thermal expansion. If the area magnification exceeds 30 times, the coefficient of thermal expansion may not be controlled within the range of the present invention, or the number of protrusions having a height of 60 nm or more may become too large. When the area magnification is less than 12 times, it tends to be difficult to obtain the coefficient of thermal expansion of the present invention.

Next, the biaxially stretched film is heat-fixed while relaxing in the width direction. As the heat fixing treatment condition, the heat fixing temperature is preferably 190 to 235 ° C, more preferably 200 to 230 ° C. It is preferable that the heat fixing temperature is divided into two or more steps and the step high temperature heat fixing is performed from the viewpoints of achieving both the temperature-humidity expansion coefficient of the present invention, controlling the number of protrusions having a height of 60 nm or more, surface roughness, and film tearing. As the conditions for the stepwise high temperature heat fixing, the first step heat fixing temperature (HS1) is preferably (stretching temperature of TD stretching 2 + 3 ° C.) to (stretching temperature of TD stretching 2 + 20 ° C.). The second stage heat fixing temperature (HS2) is preferably in the range of (HS1 + 5 ° C.) to (HS1 + 15 ° C.). The third-stage heat fixing temperature (HS3) is preferably in the range of (HS2) to (HS2 + 10 ° C.), more preferably (HS2 + 2 ° C.) to (HS2 + 10 ° C.). In order to obtain the coefficient of thermal expansion and the minute melting peak temperature (T-meta) of the present invention, it is preferable to set the heat fixing temperature of the second stage to 215 ° C. or higher, preferably 220 to 235 ° C. for easy control.

The heat fixing treatment time is preferably in the range of 0.5 to 10 seconds, and the relaxation rate is preferably 0.8 to 2.0% in the width direction. Next, the film is guided to a cooling zone adjusted to 130 to 180 ° C. and slowly cooled, and then the film edge portion is cut and wound on a roll to obtain the biaxially oriented polyester film of the present invention.

There is a difference between the stretching temperature of TD stretching 2 and the heat fixing temperature of the first stage, and if the heat fixing temperature is higher than the above range, the film is easily relaxed, it becomes difficult to obtain the coefficient of thermal expansion of the present invention, and the dimensions are stable. The sex tends to decrease. Further, the surface smoothness may be lowered, and it may be difficult to obtain the surface roughness of the present invention. On the other hand, if the heat fixing temperature is too low, the TD heat shrinkage rate cannot be controlled within the range of the present application, or the crystallinity tends to be low, and the flatness of the base film is lowered in the manufacturing process of the magnetic recording medium, and the frequency of missing pulses is generated. Tends to increase.

Next, the magnetic recording medium is manufactured as follows, for example.

The support for magnetic recording medium (biaxially oriented polyester film) obtained as described above is slit into a width of 0.1 to 3 m, for example, and conveyed at a speed of 20 to 300 m / min and a tension of 50 to 300 N / m. However, a non-magnetic paint is applied to one surface with an extraction coater to a thickness of 0.5 to 1.5 μm, and after drying, a magnetic paint is further applied to a thickness of 0.1 to 0.3 μm. Then, the support coated with the magnetic paint and the non-magnetic paint is magnetically oriented and dried at a temperature of 80 to 130 ° C. Next, a back coat is applied to the opposite surface to a thickness of 0.3 to 0.8 μm, calendar-treated, and then wound up. The calendar processing is performed using a small test calendar device (metal roll, 7 steps) at a temperature of 70 to 120 ° C. and a linear pressure of 0.5 to 5 kN / cm. Then, the pancake is aged at 60 to 80 ° C. for 24 to 72 hours and slit to a width of 12.65 mm to prepare a pancake. Next, a specific length of the pancake is incorporated into a cassette to form a cassette tape type magnetic recording medium.

Here, examples of the composition of the magnetic paint and the like include the following compositions.

Hereinafter, when simply described as "parts", it means "parts by mass".

[Magnetic layer forming coating liquid]
100 parts of barium ferrite magnetic powder [plate diameter: 20.5 nm, plate thickness: 7.6 nm, plate ratio: 2.7, Hc: 191 kA / m (≈2400 Oe) saturation magnetization: 44 Am ² / kg, BET specific surface area: 60m ² / g]
Polyurethane resin 12 parts Mass average molecular weight 10,000
Sulfonic acid functional group 0.5 meq / g
α-Alumina HIT60 (manufactured by Sumitomo Chemical Co., Ltd.) 8 parts Carbon black # 55 (manufactured by Asahi Carbon Co., Ltd.) Particle size 0.015 μm 0.5 parts Stearic acid 0.5 parts Butanone stearate 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 parts [Non- Coating liquid for forming magnetic layer]
Non-magnetic powder α iron oxide 100 parts Average major axis length: 0.09 μm, specific surface area by BET method 50 m ² / g
Average needle-like ratio: 7
DBP oil absorption: 27-38 ml / 100 g
Surface treatment layer: _Al 2 _{O 3} 8% by weight
Carbon Black 25 parts Conductex SC-U (manufactured by Colombian Carbon)
Vinyl chloride copolymer MR104 (manufactured by Nippon Zeon) 13 parts Polyurethane resin UR8200 (manufactured by Toyo Boseki) 5 parts Phenylphosphonic acid 3.5 parts Butyl stearate 1.0 parts Magnetic recording media are, for example, data recording applications, concrete Specifically, it can be suitably used for backup of computer data (for example, linear tape type recording media (LTO7, LTO8, next-generation LTO tape (LTO9)), recording of digital images such as video, and the like.

As a coating type digital recording type magnetic recording medium in which the biaxially oriented polyester film of the present invention is preferably used, for example, the magnetic layer is magnetic by uniformly dispersing ferromagnetic powder such as barium ferrite in a binder such as polyurethane resin. An example is a coating type magnetic recording medium in which a coating liquid is prepared and the coating liquid is applied to form a magnetic layer.

(Measurement method of physical properties and evaluation method of effect)
The method for measuring the characteristic value and the method for evaluating the effect in the present invention are as follows.

(1) Humidity expansion coefficient in the width direction (ppm /% RH)
In the width direction of the film, the following device is installed in a constant temperature and humidity chamber, the amount of deformation is measured under the following conditions, and the average value of the three measurement results is the coefficient of thermal expansion in the width direction in the present invention. And said.

Measuring device: Tape elongation tester 1TTM1 manufactured by Okura Industry Co., Ltd.
Constant temperature and humidity chamber: Kato Co., Ltd. TP instrumentation Version 1.04
Sample size: width 10 mm x length 200 mm (sample length)
Load: 10g
Number of measurements: 3 times Temperature: 30 ° C
Humidity condition: <1> Hold at 40% RH for 6 hours <2> Hold at 80% RH for 6 hours (humidity rate: 0.7% RH / min)
<3> Humidify to 40% RH (humidity rate: 1.4% RH / min) and hold for 6 hours <4> Humidify to 80% RH (humidity rate: 0.7% RH / min)
Measurement (L ₄₀ ): Measure the sample length after holding the humidity 40% RH for 6 hours under the humidity condition <3> (L ₄₀ ).
Measurement (L ₈₀ ): The sample length when the humidity is raised from 40% RH to 80% RH (humidity rate: 0.7% RH / min) under the humidity condition <4> is measured (L ₈₀ ).

ΔL (mm): Dimensional change amount ΔL (L _80- L ₄₀ )
The coefficient of thermal expansion (ppm /% RH) was calculated from the following equation.
Humidity expansion coefficient (ppm /% RH) = 10 6 × {(ΔL / ( sample length × humidity difference before measurement)}
Sample length before measurement = 200 (mm)
Humidity difference = 40 (%)
(2) Coefficient of thermal expansion in the width direction (ppm / ° C)
Measurements were made in the width direction of the film under a nitrogen atmosphere under the following conditions, and the average value of the three measurement results was taken as the coefficient of thermal expansion in the present invention.

Measuring device: Thermal mechanical testing machine manufactured by Vacuum Riko Co., Ltd.
TM-9400 (balance and heating furnace)
TMS-9000 (Multi Thermal Analysis Station)
Sample size: width 4 mm x length 15 mm (sample length)
Load: 5g
Number of times: 3 times Temperature: 25 ° C → 50 ° C → 20 ° C → 50 ° C (heating rate: 1 ° C / min)
Measurement (L ₀ ): Sample length at 30 ° C. when reheating (L ₀ measurement (L ₁ ): Sample length at 40 ° C. when reheating (L ₁ ))
ΔL (mm): Dimensional change amount ΔL (L ₁ −L ₀ )
The coefficient of thermal expansion was calculated from the following equation.

Temperature expansion coefficient ^{(ppm / ℃) = 10 6} × {(ΔL / ( sample length × temperature difference before measurement)}
Sample length before measurement = 15 (mm)
Temperature difference = 10 (° C)
(3) Number of protrusions with a height of 60 nm or more (pieces / mm ² )
Using a scanning white interference microscope, 100 fields of view were measured at different locations. In the sample set, the sample was set so that the Y-axis direction of the stage was the longitudinal direction of the sample film (the longitudinal direction is the direction in which the film travels in the film manufacturing process).

Measure under the following measurement conditions. The obtained image is subjected to particle analysis using the attached analysis software, a height threshold value of 60 nm is set, the number of protrusions having a height of 60 nm or more in each field of view is obtained, and the total number is ^{converted into 1 mm 2} and the height is 60 nm. The number of protrusions is as above.
[Measurement condition]
・ Equipment: Hitachi High-Tech Science Scanning White Interference Microscope VS1540
・ Objective lens: 50x ・ Wavelength filter: 530white
-Measurement mode: Wave
[Conversion processing conditions] and ・ Interpolation: Complete interpolation ・ Filter: Median 3 × 3
-Surface correction: 4th order (4) Heat shrinkage rate Measured according to JIS C2318 (1997). The sample size was prepared so that the longitudinal direction was the width direction of the film, and the heat shrinkage rate in the width direction was determined by measuring the following conditions.

Sample size: width 10 mm, marked line spacing 200 mm
Measurement conditions: Temperature 100 ° C., Processing time 30 minutes Load: No load Heat shrinkage rate (%) = [(L _0- L) / L ₀ ] x 100
L ₀ : Marked line interval before heat treatment
L: Marking line interval after heat treatment (5) Young's modulus The Young's modulus of the film was measured according to ASTM-D882 (1997). An Instron type tensile tester was used, and the conditions were as follows. The average value of the results of five measurements was taken as the Young's modulus in the present invention.

Measuring device: Instron ultra-precision material testing machine MODEL5848
Sample size:
When measuring Young's modulus in the film width direction 2 mm in the film longitudinal direction x 12.6 mm in the film width direction
(Gripping interval is 8 mm in the film width direction)
When measuring Young's modulus in the film longitudinal direction 2 mm in the film width direction x 12.6 mm in the film longitudinal direction
(Gripping interval is 8 mm in the longitudinal direction of the film)
Tensile speed: 1 mm / min Measurement environment: Temperature 23 ° C, humidity 65% RH
Number of measurements: 5 times.

(6) Fine melting peak temperature (T-meta)
According to JIS-K7121 (1987), Seiko Instruments DSC (RDC220) was used as a differential scanning calorimeter, and the company's disk station (SSC / 5200) was used as a data analyzer, and 5 mg of sample was placed on an aluminum saucer, 25. The temperature was raised from ° C. to 300 ° C. at a heating rate of 20 ° C./min. At that time, the peak temperature of the observed endothermic peak of melting was defined as the melting point (Tm), and the minute endothermic peak temperature appearing on the slightly lower temperature side of Tm was defined as T-meta. The amount of heat calculated from the peak area of Tm is defined as the amount of heat of fusion ΔHm.

(7) Surface roughness (Sa1), (Sa2)
For both sides of the film, using the device described in (3) above, measurement of 100 fields of view was performed at different locations under the same conditions, and after conversion processing was performed, the surface roughness of each field of view was roughened with the incidental analysis software. I asked for Sa. The average value of 100 visual fields was calculated for each surface, and the larger value was designated as Sa1 and the smaller value was designated as Sa2.

(8) Laminated thickness (μm)
Cross-sectional observation was carried out in 10 different fields under the following conditions, and the average value of the obtained thickness (μm) was calculated and used as the thickness (μm) of the A layer.

Measuring device: Transmission electron microscope (TEM) Hitachi H-7100FA type Measuring conditions: Acceleration voltage 100 kV
Measurement magnification: 10,000 times Sample preparation: Ultra-thin section method Observation surface: TD-ZD cross section (TD: width direction, ZD: thickness direction)
Number of measurements: Measure 3 points and 10 fields of view per field of view.

(9) Slit property When the film was slit to a width of 1 m, the slit speed was changed and the sharpness of the edge of the film was visually evaluated by the method shown below. In addition, C was judged to have poor slit property.

AA: Slitting is possible without distortion at the ends even at speeds of 70 m / min.

A: Distortion occurs at the end at a speed of 60 m / min or more and less than 70 m / min.

B: Distortion occurs at the end at a speed of 50 m / min or more and less than 60 m / min.

C: At a speed of less than 50 m / min, wrinkles are generated on the film surface and the edges are distorted.

(10) Missing pulse generation frequency A film slit to a width of 1 m is conveyed with a tension of 200 N, and a magnetic paint and a non-magnetic paint are applied to one surface of the support according to the following, and the film is slit to a width of 12.65 mm to form a pancake. create. Next, a length of 200 m from this pancake was incorporated into a cassette to obtain a magnetic tape.

(Hereinafter, "part" means "mass part".)
Coating liquid for forming a magnetic layer 100 parts of barium ferrite magnetic powder (plate diameter: 20.5 nm, plate thickness: 7.6 nm,
Plate ratio: 2.7, Hc: 191 kA / m (≈2400 Oe)
Saturation magnetization: 44Am ² / kg, BET specific surface area: 60m ² / g)
Polyurethane resin 12 parts Mass average molecular weight 10,000
Sulfonic acid functional group 0.5 meq / g
α-Alumina HIT60 (manufactured by Sumitomo Chemical Co., Ltd.) 8 parts Carbon Black # 55 (manufactured by Asahi Carbon Co., Ltd.)
Particle size 0.015 μm 0.5 part Stearic acid 0.5 part Butanone 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 parts Non-magnetic layer forming coating liquid Non-magnetic powder α Iron oxide 85 parts Average major axis length: 0.09 μm , BET method specific surface area 50m ² / g
Average needle-like ratio: 7
DBP oil absorption: 27-38 ml / 100 g
Surface treatment layer: Al ₂ O ₃ 8% by weight
Carbon Black 15 copies "Conductex" (registered trademark) SC-U (manufactured by Colombian Carbon)
Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 22 parts Phenylphosphonic acid 3 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 1 part Stearic acid 2 parts Each component of each of the above coating liquids was kneaded with a needle. The coating liquid was pumped through a horizontal sand mill containing an amount of 0.5 mmφ zirconia beads filled at 65% of the volume of the dispersion part, and stayed at 2,000 rpm for 120 minutes (substantially staying in the dispersion part). ), Distributed. To the obtained dispersion, 5.0 parts of polyisosianate was added to the paint of the non-magnetic layer, 2.5 parts was added to the paint of the magnetic layer, and 3 parts of methyl ethyl ketone was further added to obtain a filter having an average pore size of 1 μm. The coating liquids for forming the non-magnetic layer and the coating liquid for forming the magnetic layer were prepared respectively.

The obtained coating liquid for forming a non-magnetic layer is applied and dried on a PET film so that the thickness after drying is 0.8 μm, and then the coating liquid for forming a magnetic layer is applied to the thickness of the magnetic layer after drying. Is applied to 0.07 μm, and while the magnetic layer is still wet, it is oriented and dried by a cobalt magnet with a magnetic force of 6,000 G (600 mT) and a solenoid with a magnetic force of 6,000 G (600 mT). I let you. After that, the backcoat layer (carbon black average particle size: 17 nm 100 parts, calcium carbonate average particle size: 40 nm 80 parts, α-alumina average particle size: 200 nm 5 parts is made of polyurethane resin so that the thickness after calendering becomes 0.35 μm. , Dispersed in polyisocyanate) was applied. Next, the calendar was subjected to a calendar treatment at a temperature of 90 ° C. and a linear pressure of 300 kg / cm (294 kN / m), and then cured at 65 ° C. for 72 hours. Further, the non-woven fabric and the razor blade were attached to a device having a slit product feeding and winding device so as to be pressed against the magnetic surface, and the surface of the magnetic layer was cleaned with a tape cleaning device to obtain a magnetic tape.

The magnetic tape cartridge (total length of magnetic tape 500 m) obtained as described above was set in an IBM LTO-7 drive, and the magnetic tape was reciprocated 1,500 at a tension of 0.55 N and a traveling speed of 8 m / sec.

The magnetic tape cartridge after running was set in a reference drive (LTO7 drive manufactured by IBM), and the magnetic tape was run to perform recording and reproduction. The reproduced signal during traveling is taken into an external AD (Analog / Digital) conversion device, and the signal whose amplitude of the reproduced signal is reduced by 80% or more with respect to the average (average of the measured values in all tracks) is regarded as a missing pulse, and its frequency of occurrence is taken as a missing pulse. Was divided by the total length of the magnetic tape to obtain the missing pulse generation frequency (unit: times / m) per unit length of the magnetic tape. Tapes with a missing pulse generation frequency of 2.5 times / m or less were regarded as highly reliable magnetic tapes, and tapes with a missing pulse generation frequency of more than 2.5 times / m were regarded as defective, and were judged according to the following criteria. ..

AA: Missing pulse generation frequency is less than 1.5 times / m A: Missing pulse generation frequency is 1.5 times / m or more and less than 2.0 times / m B: Missing pulse generation frequency is 2.0 times / m or more , Less than 2.5 times / m C: Missing pulse generation frequency is 2.5 times / m or more.

(11) Stability of magnetic tape due to environmental changes The magnetic tape created in (10) above was set in a film size measuring device (Fig. 1) installed in a constant temperature and humidity chamber, and the load was 50 g. The width of the tape was measured under the conditions.

・ Temperature and humidity conditions <1>: 10 ° C, 10% RH
<2>: 10 ° C. 80% RH
<3>: 29 ° C. 80% RH
<4>: 45 ° C. 24% RH
<5>: 45 ° C. 10% RH
The dimensions were measured in the order of <1> → <2> → <3> → <4> → <5>, and the width of the tape was measured after leaving for 2 hours after reaching each temperature and humidity (each tape). The width is L <1>, L <2>, L <3>, L <4>, L <5>).

The tape width change between each condition is obtained, and the correction (7ppm / ° C x the temperature difference between each condition is subtracted) in consideration of the temperature expansion (7ppm / ° C) of the magnetic head is performed. The width change was calculated.

Amount of change (1) ΔL <3> -L <1> = | L <3> -L <1>-(7 × 19) |
Amount of change (2) ΔL <5> -L <2> = | L <5> -L <2>-(7 x 35) |
Of the above changes (1) and (2), the larger change is divided by the tape width (12.65 mm) and converted to ppm to be the tape width change (ppm) due to changes in the temperature and humidity environment. It was judged.

A: Less than 500ppm B: 500ppm or more and less than 800ppm C: 800ppm or more

Embodiments of the present invention will be described based on the following examples. Here, polyethylene terephthalate is referred to as PET, polyethylene naphthalate is referred to as PEN, and polyetherimide is referred to as PEI.

(1) Preparation of PET pellets: 194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, and the contents were heated to 140 ° C. to dissolve them. Then, while stirring the contents, 0.3 parts by mass of magnesium acetate tetrahydrate and 0.05 parts by mass of antimony trioxide were added, and a transesterification reaction was carried out while distilling out methanol at 140 to 230 ° C. Next, 0.5 parts by mass of a 5% by mass ethylene glycol solution of trimethyl phosphate (0.025 parts by mass as trimethyl phosphate) and 0.3 parts by mass of a 5% by mass ethylene glycol solution of monosodium dihydrogen phosphate dihydrate. By mass (0.015 parts by mass as sodium dihydrogen phosphate dihydrate) was added.

The addition of an ethylene glycol solution of trimethylphosphate lowers the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling off excess ethylene glycol. After the temperature of the reaction contents in the transesterification reactor reached 230 ° C. in this way, the reaction contents were transferred to the polymerization apparatus.

After the transition, the reaction system was gradually heated from 230 ° C. to 275 ° C. and the pressure was lowered to 0.1 kPa. The time required to reach the final temperature and the final pressure was 60 minutes. After reaching the final temperature and final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the stirring torque of the polymerization apparatus became a predetermined value (specific values differ depending on the specifications of the polymerization apparatus, but this polymerization apparatus The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 was set as a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand shape, and immediately cut to obtain PET pellets of polyethylene terephthalate having an intrinsic viscosity of 0.62 (raw material-1).

(2-a) Preparation of particle-containing PET pellets: 90 parts by mass of the above-mentioned PET pellets (raw material-1) and an average particle size of 0 were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. Supply 10 parts by mass (1 part by mass as cross-linked polystyrene particles) of 10% by mass water slurry of .45 μm cross-linked polystyrene particles, keep the vent holes at a reduced pressure of 1 kPa or less to remove water, and remove the cross-linked polystyrene particles by 1. Particle-containing pellets (raw material-2a) containing mass% and having an intrinsic viscosity of 0.62 were obtained.

(2-b) Preparation of particle-containing PET pellets: 90 parts by mass of the above-mentioned PET pellets (raw material-1) and an average particle size of 0 were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 10 parts by mass (0.5 parts by mass as cross-linked polystyrene particles) of 5% by mass water slurry of cross-linked polystyrene particles of .30 μm was supplied, and the vent holes were maintained at a reduced pressure of 1 kPa or less to remove water, and the cross-linked polystyrene particles were removed. A particle-containing pellet (raw material-2b) having an intrinsic viscosity of 0.62 containing 0.5% by mass of

(2-c) Preparation of particle-containing PET pellets: 90 parts by mass of the above-mentioned PET pellets (raw material-1) and an average particle size of 0 were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 10 parts by mass (0.5 parts by mass as cross-linked polystyrene particles) of 5% by mass water slurry of .15 μm cross-linked polystyrene particles was supplied, and the vent holes were maintained at a reduced pressure of 1 kPa or less to remove water, and the cross-linked polystyrene particles were removed. A particle-containing pellet (raw material-2c) having an intrinsic viscosity of 0.62 containing 0.5% by mass of

(2-d) Preparation of particle-containing PET pellets: 90 parts by mass of the above-mentioned PET pellets (raw material-1) and an average particle size of 0 were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 10 parts by mass (0.5 parts by mass as cross-linked polystyrene particles) of 5% by mass water slurry of .17 μm cross-linked polystyrene particles was supplied, and the vent holes were maintained at a reduced pressure of 1 kPa or less to remove water, and the cross-linked polystyrene particles were removed. A particle-containing pellet (raw material-2d) having an intrinsic viscosity of 0.62 containing 0.5% by mass of

(2-e) Preparation of particle-containing PET pellets: The above-mentioned PET pellets (raw material-1) were added to 94 parts by mass and an average particle size of 0 in a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 6 parts by mass (colloidal silica particles) of a water slurry in which glass beads having an average particle size of 0.05 mm are added to a 5 mass% water slurry of 060 μm colloidal silica particles, stirred at 1,000 rpm for 2 hours, and then filtered to remove the glass beads. 0.3 parts by mass), the vent holes are maintained at a reduced pressure of 1 kPa or less to remove water, and 0.3 mass% of colloidal silica particles are contained in particle-containing pellets having an intrinsic viscosity of 0.62 (raw material-). 2e) was obtained.

(2-f) Preparation of particle-containing PET pellets: 90 parts by mass of the above-mentioned PET pellets (raw material-1) and an average particle size of 0 in a vent-type twin-screw kneading extruder heated to 280 ° C. . 10 parts by mass (colloidal silica particles) of a water slurry in which glass beads having an average particle size of 0.05 mm are added to a 5 mass% water slurry of 20 μm colloidal silica particles, stirred at 3,000 rpm for 2 hours, and then filtered to remove the glass beads. 0.5 parts by mass), the vent holes are maintained at a reduced pressure of 1 kPa or less to remove water, and 0.5 mass% of colloidal silica particles are contained in particle-containing pellets having an intrinsic viscosity of 0.62 (raw material-). 2f) was obtained.

(2-g) Preparation of particle-containing PET pellets: 90 parts by mass of the above-mentioned PET pellets (raw material-1) and primary average particles were added to a vent-type twin-screw kneading extruder heated to 280 ° C. in the same direction. 10 parts by mass (alumina particles) of a 10% by mass water slurry of alumina particles having a diameter of 0.02 μm was added with zirconia beads having an average particle size of 0.5 mm, stirred at 3,000 rpm for 2 hours, and then filtered to remove the zirconia beads. 1 part by mass) was supplied, the vent holes were maintained at a reduced pressure of 1 kPa or less to remove water, and particle-containing pellets (raw material-2 g) containing 1% by mass of alumina particles and having an intrinsic viscosity of 0.62 were obtained. ..

(3) Preparation of two-component composition (PET / PEI) pellets: A unidirectional rotation type vent type twin-screw kneading extruder (manufactured by Japan Steel Works, Ltd.) provided with three kneading paddle kneading portions heated to a temperature of 280 ° C. , Screw diameter 30 mm, screw length / screw diameter = 45.5), and pellets of PET pellets (raw material-1) obtained by the above method and PEI "Ultem" (registered trademark) 1010 manufactured by SABIC Innovative Plastics Co., Ltd. It was fed and melt-extruded at a shear rate of 100 sec ^-1 and a residence time of 1 minute to obtain a two-component composition pellet containing 50% by mass of PEI. The glass transition temperature of the prepared two-component composition pellet was 150 ° C. (raw material-3).

(Example 1)
In the extruder E1 heated to 280 ° C. using two extruders E1 and E2, 29 parts by mass of PET pellets (raw material-1) were used as the raw material for the A layer, and the two-component composition pellets (raw material-3). 67 parts by mass of colloidal silica particle-containing pellets (raw material-2c) having an average particle size of 0.06 μm and 4 parts by mass were dried under reduced pressure at 180 ° C. for 3 hours before being supplied. Similarly, in the extruder E2 heated to 280 ° C., 28 parts by mass of PET pellets (raw material-1) and 4 parts by mass of two-component composition pellets (raw material-3) were used as the B layer raw material, and the average particle size was 0.20 μm. 64 parts by mass of colloidal silica particle-containing pellets (raw material-2e) and 4 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.30 μm were blended and dried under reduced pressure at 180 ° C. for 3 hours before being supplied. .. In order to stack two layers of these, the stacking thickness ratio (A layer | B layer) = 8 | 1 is set in the T die, and the layers are merged so that the B layer side is on the cast drum surface side, and the cast drum has a surface temperature of 25 ° C. Adhesion cooling and solidification were performed while applying an electric charge to prepare a laminated unstretched film.

This laminated unstretched film was stretched 3.3 times in the longitudinal direction (MD direction) (MD stretching 1) and 3.5 times in the width direction (TD direction) at 100 ° C. using a simultaneous biaxial stretching machine (TD stretching). 1), followed by simultaneous stretching 1.1 times in the longitudinal direction (MD stretching 2) and 1.5 times in the width direction in a heating zone at a temperature of 200 ° C. (TD stretching 2). Subsequently, while gradually raising the heat treatment temperature in the heat treatment zone in the tenter, the first stage is heat-treated at a temperature of 212 ° C. for 2 seconds, the second stage is heat-treated at a temperature of 222 ° C. for 5 seconds, and the third stage is heat-treated at 224 ° C. for 3 seconds. Was performed, and a relaxation treatment was performed in the width direction of 1.7% at a temperature of 150 ° C. Then, after cooling uniformly to 25 ° C., the film edge was removed and the film was wound on a core to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. The film-forming stability of the obtained biaxially oriented polyester film was good, and when the physical properties were evaluated, as shown in Table 4, it had excellent properties when used as a magnetic tape.

Below, the table shows the raw material composition of each Example and Comparative Example, the film forming conditions, the physical properties of the biaxially oriented polyester film, the characteristics of the magnetic tape, and the like.

(Examples 2 to 4)
A biaxially stretched polyester film having a thickness of 4.5 μm was obtained by changing the B layer raw material and stretching conditions so as to obtain the particle formulation shown in the table. The film-forming stability of the obtained biaxially oriented polyester film was good, and when the physical properties were evaluated, as shown in the table, it had excellent properties when used as a magnetic tape.

(Example 5)
In the extruder E1 heated to 280 ° C. using two extruders E1 and E2, 29 parts by mass of PET pellets (raw material-1) were used as the raw material for the A layer, and the two-component composition pellets (raw material-3). 67 parts by mass of colloidal silica particle-containing pellets (raw material-2c) having an average particle size of 0.06 μm and 4 parts by mass were dried under reduced pressure at 180 ° C. for 3 hours before being supplied. The extruder E2, which was also heated to 280 ° C., had 20 parts by mass of PET pellets (raw material-1) and 12 parts by mass of two-component composition pellets (raw material-3) as raw materials for the B layer, and had an average particle size of 0.20 μm. 64 parts by mass of colloidal silica particle-containing pellets (raw material-2e) and 4 parts by mass of crosslinked polystyrene particle-containing pellets (raw material-2a) having an average particle size of 0.30 μm were blended and dried under reduced pressure at 180 ° C. for 3 hours before being supplied. .. In order to stack two layers of these, the stacking thickness ratio (A layer | B layer) = 8 | 1 is set in the T die, and the layers are merged so that the B layer side is on the cast drum surface side, and the cast drum has a surface temperature of 25 ° C. Adhesion cooling and solidification were performed while applying an electric charge to prepare a laminated unstretched film.

This laminated unstretched film was stretched 3.1 times in the longitudinal direction (MD direction) (MD stretching 1) and 3.5 times in the width direction (TD direction) at 100 ° C. using a simultaneous biaxial stretching machine (TD stretching). 1), followed by simultaneous stretching 1.1 times in the longitudinal direction (MD stretching 2) and 1.6 times in the width direction in a heating zone at a temperature of 200 ° C. (TD stretching 2). Subsequently, while gradually raising the heat treatment temperature in the heat treatment zone in the tenter, the first stage is heat-treated at a temperature of 212 ° C. for 2 seconds, the second stage is heat-treated at a temperature of 222 ° C. for 5 seconds, and the third stage is heat-treated at 224 ° C. for 3 seconds. Was performed, and a relaxation treatment was performed in the width direction of 1.7% at a temperature of 150 ° C. Then, after cooling uniformly to 25 ° C., the film edge was removed and the film was wound on a core to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. The film-forming stability of the obtained biaxially oriented polyester film was good, and when the physical properties were evaluated, as shown in Table 4, it had excellent properties when used as a magnetic tape.

(Comparative Example 1)
As shown in the table, the stretching conditions were changed to obtain a biaxially stretched polyester film having a thickness of 4.5 μm.

(Comparative Example 2)
Using the raw materials used as the particle formulations shown in the table, they were dried under reduced pressure at 180 ° C. for 3 hours before being supplied. In order to stack two layers of these, the stacking thickness ratio (A layer | B layer) = 4 | 1 is set in the T die, and the layers are merged so that the B layer side is on the cast drum surface side, and the cast drum has a surface temperature of 25 ° C. Adhesion cooling and solidification were performed while applying an electric charge to prepare a laminated unstretched film.

This laminated unstretched film was stretched 3.5 times in the longitudinal direction in three steps at 90 ° C. using a roll-type stretcher. This stretching was performed at 2.5 times in the first stage, 1.34 times in the second stage, and 1.05 times in the third stage using the difference in peripheral speed between the two sets of rolls.

While grasping both ends of the obtained uniaxially stretched film with clips, the film is guided to a preheating zone having a temperature of 95 ° C. in the tenter, and continuously in a heating zone having a temperature of 90 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Was stretched 3.5 times (TD stretch 1), and subsequently stretched 1.4 times in the width direction in a heating zone at a temperature of 195 ° C. (TD stretch 2). Subsequently, the heat treatment zone in the tenter was heat-treated at a temperature of 190 ° C. for 10 seconds, and further relaxed at a temperature of 150 ° C. in the 0.5% width direction. Then, after cooling uniformly to 25 ° C., the film edge was removed and the film was wound on a core to obtain a biaxially stretched polyester film having a thickness of 4.5 μm.

(Comparative Example 3)
A biaxially stretched polyester film having a thickness of 4.4 μm was obtained by changing the raw material, stretching conditions, and heat fixing temperature so as to obtain the particle formulations shown in the table.

(Comparative Example 4)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 2 except that the heat fixing temperature was changed.

(Comparative Example 5)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 1 except that the heat fixing temperature was changed.

(Comparative Example 6)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 4 except that the stretching conditions and the heat fixing temperature were changed.

1: Laser transmitter 2: Receiver 3: Load detector 4: Load 5-8: Free roll 9: Magnetic tape 10: Laser light

Claims (7)

The coefficient of thermal expansion in the width direction is 4.5 to 6.5 ppm /% RH, the coefficient of thermal expansion in the width direction is -3.0 to 7.0 ppm / ° C, and the height is at least one of the outermost layer surfaces. A biaxially oriented polyester film having a number of protrusions of 60 nm or more of 0 to 200 / mm ^2. The biaxially oriented polyester film according to claim 1, wherein the heat shrinkage rate in the width direction is 1.0% or less. The biaxially oriented polyester film according to claim 1 or 2, wherein the Young's modulus in the width direction is 7.0 to 12.0 GPa. The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the minute melting peak temperature (T-meta) is 210 to 240 ° C. The biaxially oriented polyester film according to any one of claims 1 to 4, wherein at least one surface roughness (Sa1) is 3.0 to 7.0 nm. The biaxially oriented polyester film according to claim 5, wherein the surface roughness (Sa2) of the outermost layer surface on the side opposite to the surface constituting Sa1 is 0.5 to 5.0 nm. The biaxially oriented polyester film according to any one of claims 1 to 6, which is used as a base film for a coating type digital recording type magnetic recording medium.

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